What is Home Battery Storage?

Basically these are battery packs like used in EVs but for your home power. They can be used with or without solar, but the rebates only apply when used with solar.

Will Home Battery storage save me money?

It depends on your utility! For example if your utility charges time-of-use rates you can use the battery to run your house during high rate hours then charge the battery off-peak hours. Also if your utility doesn’t offer solar net metering it allows you to take full advantage of the solar power you generate.

But at least for major Western Washington utility users (PSE, Seattle City Light, and Tacoma Power) these aren’t a concern.

Can it make me greener?

Probably not. There’s two fundamental usage scenarios – avoiding grid power and outage recovery.

The concept of avoiding grid power sounds great – use the solar power you create during the day to power your home at night. But the reality is its a wash. If I don’t store excess solar production in a battery it goes to the grid so my neighbor uses it and PSE burns less coal/natural gas because of that solar production. That overproduction then gets me credits which I then use to pull from the grid at night (which may be greener at night…but that’s complicated). The net effect is the same as if I stored my own solar power during the day and used that power at night.

Now for the outage recovery scenario – is a grid or solar powered battery greener than a gas generator? My knee-jerk reaction was “hell yes” but then I remembered that while running a solar or grid powered battery is greener than running a gas engine – manufacturing the battery is dirtier. This nets out in favor of the battery in EVs because of significant usage, but with light use a generator (especially propane) will likely have a lesser environmental impact than home battery storage.

How good is a home battery for outages?

Battery power kicks in faster than a generator and has super clean power, so for those aspects they’re great. Capacity is the complex matter. Each Tesla Powerwall has 13.5kwh of capacity – enough to run the average NW home for about half a day. Now where things get fun (and complex) is when you tie multiple Powerwalls together and add solar. At that point you can run off grid forever-ish which will make you Mr. Popular after an earthquake.

So why forever-ish? Seattle has particularly great summers for solar and bad winters. A solar array that can run your whole home in the summer may only be able to power the gas furnace and a fridge in the winter. Still better than nothing but don’t expect to be hot tubbing. On the flip side if you’re in San Diego winter output is much better so enjoy that hot tub on those chilly 65 degree winter nights.

What about cost?

Right now in the Seattle area expect to pay $11-14k after federal rebate to get one Powerwall installed and about $4000 for additional units. The value of course depends to what you’re comparing. A whole home standby generator runs in the same ballpark but only has unlimited fuel if the natural gas keeps flowing, which it may not after an earthquake. Of course you can always spend even more money and make space for a storage tank. Just spitballing but batteries plus solar looks like it should have a much lower lifetime cost. On the flip side it’s hard to beat the cost of a $600 portable generator from Costco assuming you don’t mind tending to it manually and have gas or propane available when needed.

Will it get cheaper?

Hard to say. A significant percentage of the cost is labor as it takes two Electricians a couple days to install. That install time will hopefully streamline a bit in time, but it’s a big limiting factor on total system cost. Batteries tend to get cheaper over time, but current demand is so high Tesla raised prices. And the Federal 30% rebate decreases soon, so unless Trump can be fooled into thinking the Powerwall is coal powered we’re not likely to see an immediate improvement of this rebate.

How long will it last?

The Powerwall has a 10 year warranty with no cycle limit which is a pretty stellar warranty. Battery capacity decreases with charge/discharge cycles so daily use will affect capacity and lifespan more than if you’re just using it for outages.

Who’s it good for?

A niche group of people and business. Imagine you have a medically sensitive family member and unlimited power backup sounds great. Convenience and disaster planning are good reasons too. Businesses that always need power or they’ll suffer significant financial losses can also benefit.

What’s the Bottom Line?

Most people won’t benefit from getting home battery storage and it probably isn’t greener. The value and appeal of battery storage will vary depending on how often you have outages, for how long those outages last, and how much impact an outage has on your family or business.